Process for separating carbon from iron-bearing fines in blast furnace flue dusts

ABSTRACT

Carbon particles can be separated from iron oxide particles and other gangue particles contained in blast furnace flue dust. The blast furnace flue dust is mixed with water to form a slurry containing 50 percent to 70 percent solids. A flotation agent and a forthing agent are added to the slurry. The slurry is vigorously agitated to thoroughly coat the carbon particles with the flotation agent. The slurry is diluted and passed to flotation cells. The carbon particles float on the surface of the slurry and the iron oxide particles and other gangue particles do not float atop the slurry. The carbon particles are collected as a float product while the iron oxide particles and other gangue particles are collected as a sink product.

United States Patent Lynn et a1.

[5 PROCESS FOR SEPARATING CARBON FROM IRON-BEARING FINES 1N BLASTFURNACE FLUE DUSTS [75] Inventors: John D. Lynn, Center Valley; James L.Sloughfy, Bethlehem, both of Pa.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

221 Filed: Jan. 18, 1912 211 App]. No.: 218,828

[52] US. Cl. 241/24, 209/166 [51] B03d 1/02 [58] Field of Search209/166, 167, 3,

[56] References Cited UNITED STATES PATENTS 1,329,493 2/1920 Bacon209/166 1,552,197 9/1925 Bates 209/166 1,787,938 1/1931 Eisele 209/1661,840,267 1/1932 Tschudy 209/166 1,984,386 12/1934 Tschudy 209/166 UXNov. 6, 1973 Primary ExaminerR0bert Halper Attorney.loseph J. OKeefe[57] ABSTRACT Carbon particles can be separated from iron oxideparticles and other gangue particles contained in blast furnace fluedust. The blast furnace flue dust is mixed with water to form a slurrycontaining 50 percent to 70 percent solids. A flotation agent and aforthing agent are added to the slurry. The slurry is vigorouslyagitated to thoroughly coat the carbon particles with the flotationagent. The slurry is diluted and passed to flotation cells. The carbonparticles float on the surface of the slurry and the iron oxideparticles and other gangue particles do not float atop the slurry. Thecarbon particles are collected as a float product while the iron oxideparticles and other gangue particles are collected as a sink product.

14 Claims, No Drawings 1 PROCESS FOR SEPARATING CARBON FROMIRON-BEARINGFINES IN BLAST FURNACE FLUE DUSTS Y BACKGROUND OF THEINVENTION This invention in general is directed to a method forseparating carbon particles from iron oxide particles and gangueparticles. More specifically, the invention is directed to a method forseparating carbon particles from iron oxide particles and gangueparticles contained in blast furnace flue dusts and to recover thecarbon particles as a float product and to recover the iron oxideparticles and gangue particles as a sink product which can be pelletizedand charged into a metallurgical furnace. The carbon content of the sinkproduct is reduced to a minimum.

Prior art practices to treat blast furnace flue dusts which containcarbon particles, iron oxide particles and gangue particles includepassing a slurry of flue dusts to froth-flotation cells wherein thecarbon particles are floated and recovered as a float product and theiron oxide particles and gangue particles are recovered as a sinkproductpThe priorart practices are exemplifiedin u.s. Pat. No. 1,984,386issued Dec. 18, 1934 to Frederich Tschudy and entitled, Process ofSeparating Composite Materials. Such processes are partially successful.However, the amount of carbonremaining in the sink product with the ironoxide particles and gangue particles is more than about percent. Thisamount of carbon negates the recovery of the iron oxide particles as aballed and pelletized product. The amount of carbon in the sink productand consequently in the balled product is sufficient to causeoverheating and fusion of the balls during heating for pelletization.The result is a clinker-type product rather than discrete pellets asdesired. I

It is an object of this invention to provide a method for separatingcarbon particles from iron oxide particles and gangue particles in amaterial containing said particles.

It is an object of this invention to provide a method for separating thecarbon particles in wet blast furnace flue dusts from iron oxideparticles and gangue particles contained therein.

It is an object of this invention to provide a method for separating thecarbon particles in dry blast furnace flue dusts from iron oxideparticles and gangue particles contained therein.

It is an object of this invention to provide a method for separating thecarbon particles in mixtures of wet and dry blast furnace flue dustsfrom iron oxide particles and gangue particles contained therein.

It is an object of this invention to'provide a method for separating thecarbon particles of wet, dry, and mixtures of blast furnace flue dustscontaining iron oxide particles and gangue particles, wherein said blastfurnace flue dusts are subjected to froth-flotation and the carbonparticles collected as a float product can be used as a fuel and theiron oxide particles and gangue particles collected as a sink producthave a carbon content of not more than about 5 percent can be balled,pelletized, and/or metallized and used as charge materials in furnaces,for example, a blast furnace, electric furnace, open hearth furnace,basic oxygen furnace.

PREFERRED EMBODIMENT OF THE INVENTION It has been found that wet or dryblast furnace flue dusts and mixtures thereof, which contain carbonparticles, iron oxide particles and gangue particles can be treated toseparate the carbon particles from the iron oxide particles and gangueparticles. The carbon content of the iron oxide and gangue particles canbe reduced to below about 5 percent.

The method of the invention has been found to be applicable to allmixtures of blast furnace flue dusts from 100 percent wet blast furnaceflue dusts to 100 percent dry blast furnace flue dusts but it ispreferred to use mixtures of about 25 percent wet blast furnace fluedusts and 75 percent dry blast furnace flue' dusts to 75 percent wetblast furnace flue dusts and 25 percent dry blast furnace flue dusts.

Blast furnace flue dusts can contain, for example, about to about 50percent carbon, about to about 55 percent total iron of which'as much as60 percent is in the form of Fe o about 5 percent to about 8.5 percentsilica, about 1.0 to about 2.0 percent alumina, about 4.0'to about 6.0percent calcium oxide and about 1.0 to about 2.5 percent magnesia. Theblast furnace flue dusts are mixed with water to form a slurry having Ia pulp density of about 50 to about 70 percent solids.

Hereinafter whenever sieve sizes are mentioned the sieves are of theTyler series. The particles of the blast furnace flue dusts should be 28mesh when added to water to form such a slurry. Particles of wet blastfurnace flue dusts generally are 28 mesh size, therefore, they can beused as received. Dry blast furnace flue dusts on the other hand cancontain particles which are +28 mesh size, therefore, a sizeseparation-is made at 28 mesh. The +28 mesh size particles are ground toa 28 mesh size. The separation at 28 mesh is made to preventovergrindingthe 28 mesh size particles which are in the dry blastfurnace flue dusts. Of course, it is possible to add the dry blastfurnace flue dusts to the wet blast furnace flue dusts prior to grindingbut .to prevent overgrinding of the 28 mesh size particles con-' ferredto as MIBC) or a pine oil and the like. It is preferred to use No. 2fuel oil as the flotation agent and MIBC as the frothing agent. It hasbeen found that from about 0.5 of a pound to about 35 pounds of No. 2fuel oil per dry ton of flue dusts in the slurry and about 0.06 of apound to about 0.30 of a pound of MIBC per dry ton of flue dusts in theslurry are added to the slurry to obtain the results of the invention.The amount of flotation agent and frothingiagent added to the slurry isalways on a dried flue dust basis although the slurry can contain wetand dry flue dusts.

The slurry is violently agitated in an appropriate apparatus. Theviolent agitation is necessary so that the immiscible flotation agentand water are mixed and discrete droplets of the flotation agent formedduring agitation will come into contact with the particles in the about4 minutes to achieve good results but for better results about 5 minutesof agitation is necessary. Of course, agitation times less than 4minutes will result in the separation of some carbon particles duringsubsequent flotation. However, carbon contents greater than 5 percentwill remain in the sink product. However, lengthy agitation times do notimprove the results of the invention, therefore such lengthy times wouldnot be economical. It is preferred to agitate the slurry between about 4minutes to about'6 minutes. Any appropriate apparatus can be used toagitate the slurry but it is preferred to use a mixer having a stirrerrotating at relatively high speeds. While the speed and time ofagitation are essential, they are merely indicative of the agitationdesired in the method of the invention. The most important factor is theamount of heat energy formed in the slurry during agitation. The heatenergy formed in a volume of slurry is greater than the heat energyformed in an equal volume of water substantially free of solids which isagitated under the same conditions as the slurry. The slurry can contain50 to 70 percent solids which contain carbon, iron and other particles.Obviously, the amount and type of particles in the slurry will have anaffect on the ease of agitation. To provide a basis for the amount ofheat energy required to obtain the desired agitation an equal volume ofwater substantially free of solids was used. The water was agitatedunder the same conditions as the slurry. The heat energy so formed inthe water is between about 0.25 calories per gram of water per minute toabout 0.40 calories per gram of water per minute. It will be understoodthat hereinafter wherever heat energy is referred to such heat energy ispredicated on the agitation of an equal volume of water substantiallyfree of solids. The use of agitators which create heat energy lower than0.25 calories per gram of water per minute do not achieve the degree ofcarbon separation which is desired. Agitators which create heat energygreater than 0.40 calories per gram of water per minute do result inobtaining the desired carbon separation. However, the degree of carbonseparation is not any better than achieved with agitators which createheat energy of 0.40 calories per gram of water per minute. Therefore,the use of the more rigorous agitators is wasteful of electrical powerwhich is used to operate the agitators.

After agitation the pulp density of the slurry is adjusted by addingwater thereto to obtain a slurry containing about to about 35 percentsolids. The slurry is passed to froth-flotation cells, for example,Denver Sub A flotation cells. Air is bubbled upwardly through the slurryin the froth-flotation cells. The carbon particles are floated to thetop of the slurry by the air while the iron oxide particles and gangueparticles remain suspended in the slurry in the cells. Of course, it isvirtually impossible to prevent very small iron oxide particles andgangue particles from being floated into the froth. However, the amountof such particles in the froth is negligible. It is also true that somecarbon particles will remain suspended in the slurry with the iron oxideparticles and gangue particles but the percentage of such particles isrelatively small. It must be recognized that water and MIBC are lostduring froth removal. It is, therefore, necessary to add water tomaintain the level of the slurry in the cells so that the froth can beremoved therefrom while still maintaining the pulp density of the slurryat about 10 to about 35 percent solids. About 0.03 of a pound of MIBCper ton of dry feed solids is added from time to time to maintain, asufficient amount thereof in the slurry whereby efficient removal ofcarbon particles is realized. Usually, the time interval between MIBCadditions is, between about 2 minutes to about 4 minutes of operatingtime. In the method of the invention about to about percent of thecarbon originally contained in the blast furnace flue dusts is recoveredas a float product and an iron oxide concentrate containing from about0.75 to not more than about 5 percent carbon is recovered as a sinkproduct. The float product can contain as much as 15 percent impurities,such as silica, alumina, magnesia and the like.

Wherever percentages are recited in this specification and claims suchpercentages are on a weight basis unless otherwise noted.

In a specific example of the invention a sample of dry blast furnaceflue dust was screened at 28 mesh to separate the +28 mesh particlesfrom the 28 mesh particles. The +28 mesh particles were ground so thatpercent of the particles passed a 28 mesh sieve. The ground particlesand the original 28 mesh particles were then mixed. The blast furnaceflue dust so treated had the following analysis:

CHEMICAL ANALYSIS (9%) II F61 24.9 *Fe total iron SiO, 8.4

CaO 7. l

About 414 grams of the dry blast furnace flue dust was mixed with 400ml. of water to obtain a slurry having a pulp density of 51 percentsolids. The slurry was conditioned by adding 3.9 pounds of No. 2 fueloil per ton of dry flue dust and 0.03 of a pound of MIBC per ton of dryflue dust. The conditioned slurry was violently agitated in a mixerhaving an impeller speed of 1,800 rpm for 5 minutes and passed to DenverSub A flotation cells. The heat energy in the slurry was found to beequivalent to about 0.25 calories per gram of water per minute. Theslurry was diluted by adding 1400 ml. of water, thereto to adjust thepulp density to 18.7 percent solids. Air was bubbled upwardly throughthe slurry in the flotation cells. After 2 minutes of operation, 0.03 ofa pound of MIBC per ton of dry flue dust was added to the slurry.Thereafter, 0.03 of a pound of MIBC per ton of dry flue dust was addedto the slurry at 4 minute intervals until the end of the run. Water wasadded from time to time to maintain the slurry level in the cell. Thefloat product referred to as a carbon concentrate and the sink productreferred to as the iron concentrate were collected and dried. Thechemical analyses of the concentrates are shown below:

Total iron content. Free carbon content.

Note that the carbon concentrate, that is, the float product contains98.6 percent of the carbon in the original flue dust and only 12.8percent of the iron oxides.

in another specific example of the invention, wet

was mixed with water to form a slurry having a pump density of 5lpercent as in the first specific example. The slurry was conditioned andsubjected to the frothflotation process as described in the firstspecific example. The chemical analyses of the carbon concentrate andiron concentrate are shown below:

d. agitating the slurry for a time not less than 4 minutes wherein heatenergy formed in the slurry is greaterthan the heat energy formed byagitating an equal volume of water under the same conditions as theslurry, g I

e. diluting the slurry to a pump density of about 10 to about 35 percentsolids,

f.'passing the slurry to froth-flotation cells,

g. bubbling air upwardly through the slurry for a time to selectivelyfloat substantially all the carbon particles into a froth formed atopthe slurry while substantially all the iron oxide particles and gangueparticlesremain suspended in the slurry, and

h. removing the carbon particles as a float product and the iron oxideparticles and gangue particles as a sink product from thefroth-flotation cells.

2. The method of claim 1 in which the flotation agent Percent Analysis(Percent) distribution Fe C SiOz A1203 Ca0 MgO I F' C Carbon Concentrate8.8 70.4 4.2 1.6 2.3 1.1 18.2 97.6 Iron Concentrate 46.0 2.0 12.8 1.38.9 2.7 81.8 2.4

In a third specific example, a mix consisting of percent of the screenedground and remixed dry blast furnace flue dust of the first specificexample and 50 percent of the wet blast furnace flue dust of the secondspecific example was made. A chemical analysis of the mix follows:

CHEMICAL ANALYsIs CaO 6.1

MgO 2.2

SiO

A slurry of the mix was made and conditioned as in the first specificexample. The conditioned slurry was sub- 1 jected to the froth-flotationprocess of the firstspecific 5 example. The chemical anslyse's of thecarbon concentrate and iron concentrate recovered in the froth- 4Oflotation process follows:

added to the slurry in step (c) is No. 2 fuel oil 3. The method of claim1 in which the frothing agent added to the slurry in step (c) ismethylisobutylcarbinol.

4. The method of claim 2 in which the frothing agent added to the slurryin step (c) is methylisobutylcarbinol.

(Percent) Analysis (percent) distribution Fe C S102 A1 0: 0210 MgO Fe CCarbon concentrate 8. 2 70 5 4. 5 1. 8 2. 5 1. 1 17. 2 98. 0 Ironconcentrate 44. 6 1. 6 11. 6 1. 9 10.1 3. 4 82. 8 2. 0

i We claim:

gram of water per minute.

Improved method for treating blast furnace flue I 7. Improved method fortreating dry blast furnace dusts by froth-flotation to separatesubstantially all the carbon particles from iron oxide particles andgangue particles contained therein, said carbon particles beingrecovered as a float product and said iron oxide particles and gangueparticles being recovered as a sink product containing not more than 5percent carbon, said method comprising:

a. reducing substantially all the particles in the blast furnace fluedusts to a 28. mesh size, b. adding the blast furnace flue dusts towater to for a slurry having a pump density of about 50 to about percentsolids,

c. adding at least one flotation agent taken from the group consistingof No. 2 fuel oil and kerosene, and

at least one frothing agent taken from the group consisting ofmethylisobutylcarbinol and pine oil, to the slurry,

flue dusts by froth flotation to separate substantially all the carbonparticles from iron oxide particles and gangue particles containedtherein, said carbon particles being removed as a float product and saidiron oxide particles and gangue particles being removed as a sinkproduct containing not more than 5 percent carbon, said methodcomprising:

7 aTEFrEiIEgTHe'T'J blast furnace flue dust to obtain a particle sizeseparation at 28 mesh, I

b. grinding the particles larger than 28 mesh toa size smaller than 28mesh,

c. mixing the particles smaller than 28 mesh of step (a) and of step(b),

d. forming a slurry of the particles of step (c) and water, said slurryhaving a pump density of about 50 percent to about 70 percent solids,

"f. agitating the slurry for a time not less than 4 minutes wherein heatenergy created in the slurry is equivalent to not less than about 0.25calories per gram of water per minute,

g. diluting the slurry to a pump density of about to about 35 percentsolids,

h. passing the slurry to froth-flotation cells,

i. bubbling air upwardly through the slurry for a time to selectivelyfloat substantially all. the carbon particles in a froth formed atop theslurry, while substantially all the iron oxide particles and gangueparticles remain suspended in the slurry, and

j. removing the carbon particles as a float product and the iron oxideparticles and gangue particles as a sink product from thefroth-flotation cells.

8. The method of claim 7 in which the flotation agent added in step (e)is No. 2 fuel oil.

9. The method of claim 7 in which the frothing agent added in step (e)is methylisobutylcarbinol.

10. The method of claim 8 in which the frothing agent added in step (e)is methylisobutylcarbinol.

11. Improved method for treating wet blast furnace flue dusts byfroth-flotation to separate substantially all the carbon particles fromiron oxide particles and gangue particles contained therein, said carbonparticles being removed in a froth as afloat product and said iron oxideparticles and gangue particles being removed as a sink productcontaining about 0.75 to about 5 percent carbon, said method comprising:

a. forming a slurry of water and wet blast furnace flue dusts having apump density of about 50 to about percent solids,

b. adding at least one flotation agent taken from the group consistingof No. 2 fuel oil and kerosene, and at least one frothing agent takenfrom the group consisting of methylisobutylcarbinol and pine oil, to theslurry,

c. agitatin the slurry for a time not less than 4 minutes wherein a heatenergy created in the slurry is equivalent to not less than 0.25calories per gram of water per minute,

(1. diluting theslurry to a pump density of about 10 to about 35 percentsolids,

e. passing the slurry to froth-flotation cells,

f. bubbling air upwardly through the slurry for a time to selectivelyfloat substantially all the carbon particles in the slurry to the frothformed atop the slurry while substantially all the iron oxide particlesand gangue particles remain suspended in the slurry, and

g. removing substantially all the carbon particles as a float productand substantially allthe iron oxide particles and gangue particles as asink product.

12. The method of claim 11 in which the flotation agent added in step(b) is No. 2 fuel oil.

13. The method of claim 11 in which the frothing agent added in step (b)is methylisobutylcarbinol.

14. The method of claim 12 in which the frothing agent added in step (b)is methylisobutylcarbinol.

2. The method of claim 1 in which the flotation agent added to theslurry in step (c) is No. 2 fuel oil.
 3. The method of claim 1 in whichthe frothing agent added to the slurry in step (c) ismethylisobutylcarbinol.
 4. The method of claim 2 in which the frothingagent added to the slurry in step (c) is methylisobutylcarbinol.
 5. Themethod of claim 1 in which the heat energy formed when a volume of waterequal to a volume of slurry is agitated in step (d) is not less thanabout 0.25 calories per gram of water per minute.
 6. The method of claim1 in which the flotation agent of setp (c) is No. 2 fuel oil, thefrothing agent of step (c) is methylisobutylcarbinol, the time ofagitation of step (d) is not less than 4 minutes and the heat energyformed in step (d) is not less than 0.25 calories per gram of water perminute.
 7. Improved method for treating dry blast furnace flue dusts byfroth-flotation to separate substantially all the carbon particles fromiron oxide particles and gangue particles contained therein, said carbonparticles being removed as a float product and said iron oxide particlesand gangue particles being removed as a sink product containing not morethan 5 percent carbon, said method comprising: a. screening the dryblast furnace flue dust to obtain a particle size separation at 28 mesh,b. grinding the particles larger than 28 mesh to a size smaller than 28mesh, c. mixing the particles smaller than 28 mesh of step (a) and ofstep (b), d. forming a slurry of the particles of step (c) and water,said slurry having a pump density of about 50 percent to about 70percent solids, e. adding at least one flotation agent taken from thegroup consisting of No. 2 fuel oil and kerosene, and at least onefrothing agent taken from the group consisting of methylisobutylcarbinoland pine oil, to the slurry, f. agitating the slurry for a time not lessthan 4 minutes wherein heat energy created in the slurry is equivalentto not less than about 0.25 calories per gram of water per minute, g.diluting the slurry to a pump density of about 10 to about 35 percentsolids, h. passing the slurry to froth-flotation cells, i. bubbling airupwardly through the slurry for a time to selectively floatsubstantially all the carbon particles in a froth formed atop theslurry, while substantially all the iron oxide particles and gangueparticles remain suspended in the slurry, and j. removing the carbonparticles as a float product and the iron oxide particles and gangueparticles as a sink product from the froth-flotation cells.
 8. Themethod of claim 7 in which the flotation agent added in step (e) is No.2 fuel oil.
 9. The method of claim 7 in which the frothing agent addedin step (e) is methylisobutylcarbinol.
 10. The method of claim 8 inwhich the frothing agent added in step (e) is methylisobutylcarbinol.11. Improved method for treating wet blast furnace flue dusts byfroth-flotation to separate substantially all the carbon particles fromiron oxide particles and gangue particles contained therein, said carbonparticles being removed in a froth as a float product and said ironoxide particles and gangue particles being removed as a sink productcontaining about 0.75 to about 5 percent carbon, said method comprising:a. forming a slurry of water and wet blast furnace flue dusts having apump density of about 50 to about 70 percent solids, b. adding at leastone flotation agent taken from the group consisting of No. 2 fuel oiland kerosene, and at least one frothing agent taken from the groupconsisting of methylisobutylcarbinol and pine oil, to the slurry, c.agitatin the slurry for a time not less than 4 minutes wherein a heatenergy created in the slurry is equivalent to not less than 0.25calories per gram of water per minute, d. diluting the slurry to a pumpdensity of about 10 to about 35 percent solids, e. passing the slurry tofroth-flotation cells, f. bubbling air upwardly through the slurry for atime to selectively float substantially all the carbon particles in theslurry to the froth formed atop the slurry while substantially all theiron oxide particles and gangue particles remain suspended in theslurry, and g. removing substantially all the carbon particles as afloat product and substantially all the iron oxide particles and gangueparticles as a sink product.
 12. The method of claim 11 in which theflotation agent added in step (b) is No. 2 fuel oil.
 13. The method ofclaim 11 in which the frothing agent added in step (b) ismethylisobutylcarbinol.
 14. The method of claim 12 in which the frothingagent added in step (b) is methylisobutylcarbinol.